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Vent Calculator

Quick Vent Calculation Guide for O’Hagin’s Standard, WeatherMaster™, and Fire & Ice® Attic Vents

There are two important pieces of information required in order to calculate the adequate number of vents required for your project:

  1. Determine the total square footage of the attic floor space to be ventilated.
  2. You must know which code compliance method is required in the project area. Most local building codes require compliance with either the 1/150 method or the 1/300 method exception (refer to local code). These methods dictate that one (1) square foot of ventilation is provided for every 150 or 300 square feet of attic floor space. Compliance with attic ventilation code requirements should always be verified at the local governing level before performing the following calculations.

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Step 1: DETERMINE SQUARE FEET OF CODE-REQUIRED VENTILATION

Square Feet:

÷ Compliance Method

Calculate
=
Total Square Feet of Code Required Ventilation

Step 2: CONVERT SQUARE FEET OF CODE-REQUIRED VENTILATION TO SQUARE INCHES

x 144 = Total Square inches of Code-Required Ventilation

Step 3: DETERMINE THE ADEQUATE NUMBER OF O’HAGIN VENTS REQUIRED

Total Vents Required for sq. inches:

Tapered Low-Profile
72.0 sq. in NFVA

Vents High:
Vents Low:

High-Profile Model S
97.5 sq. in NFVA

Vents High:
Vents Low:

Low/Medium Profile Model M
86.25 sq. in NFVA

Vents High:
Vents Low:

Low-Profile Model Flat
98.75 sq. in NFVA

Vents High:
Vents Low:

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MANUFACTURER’S RECOMMENDATIONS
The patented O’Hagin Balanced Ventilation System utilizes O’Hagin vents placed strategically within the field of roofing material both high (near the ridge for exhaust) and low (near the eave for intake). This strategic high and low placement of O’Hagin vents allows the balanced system to fully optimize both wind and thermal effects to provide superior passive ventilation throughout the attic. Additionally, placement of O’Hagin vents both high and low should provide an equal, balanced rate of ventilation performance in each area. The calculations above do not include any potential Net Free Ventilation Area (NFVA) values provided by alternative ventilation methods that may be present in any specific structural design.

Vent Calculator

Step 1: DETERMINE SQUARE FEET OF CODE-REQUIRED VENTILATION

Square Feet:

÷ Compliance Method:

=

Total Square Feet of Code Required Ventilation

Step 2: CONVERT SQUARE FEET OF CODE-REQUIRED VENTILATION TO SQUARE INCHES

x 144 = Total Square inches of Code-Required Ventilation

Step 3: DETERMINE THE ADEQUATE NUMBER OF O’HAGIN VENTS REQUIRED

Total Vents Required for sq. inches:

Tapered Low-Profile
72.0 sq. in NFVA

Vents High:
Vents Low:

High-Profile Model S
97.5 sq. in NFVA

Vents High:
Vents Low:

Low/Med Profile Model M
86.25 sq. in NFVA

Vents High:
Vents Low:

Low-Profile Model Flat
98.75 sq. in NFVA

Vents High:
Vents Low: